1. FIELD OF THE INVENTION
The invention concerns a process for the recovery of lead from lead batteries which are to be scrapped, wherein the batteries are broken up by a single stage or multi-stage mechanical comminution process and freed from battery acid, as well as apparatus for carrying out the process.
2. DESCRIPTION OF THE PRIOR ART
Processes of this type have been known for a long time. In these processes, e.g. as described in German Patent Specification No. 1,224,935, the batteries are freed from the battery acid and broken or coarsely comminuted and are then fed to an impact mill to be broken into, essentially, grid pieces, coarse to fine particles of grid lead and broken pieces of the poles or terminals and cell connectors; electrode paste of fine particle size; and coarsely broken pieces of the separators and the housing. This battery scrap is then separated by numerous screening and other mechanical or physical separation processes into, essentially, plastics parts, coarse metallic pieces, and fine particle sized components which consist essentially of lead oxide and lead sulphate as well as pure lead powder from the electrode fill.
The component of fine particle size is then reduced to lead in a reduction oven at temperatures of 800.degree. to 1000.degree. C by smelting with coal. The lead corresponds in quality however only to average crude lead with a relatively high content of antimony, which in this form is unsuitable for the manufacture of new batteries. In order to recover lead suitable for the manufacture of new batteries in principle two possibilities exist: one can fuse the crude lead with the coarse pieces of the grid and the terminals and cell connectors and obtain a lead-antimony alloy the antimony content of which is about 50% of that required in grid lead for new batteries and which has to be brought to the antimony content required by alloying with antimony. This possibility, which at first sight appears relatively simple has a number of disadvantages. Thus the result of the costly separation process, namely the division on the one hand into fine particle size components which in the main consist of pure lead and lead compounds, and on the other hand into broken pieces of grid lead, terminals and cell connectors and thus of hard antimonial lead, is for the most part negated. The remaining advantage of the separation is then merely that only about one-half of the material needs to be smelted in the reduction oven. The need for additional antimony for alloying, and particularly the consequential need for expensive pure lead to construct new batteries, are to be seen as very considerable disadvantages. A further significant disadvantage is economic: one can only proceed in this way when the recycling ratio of used batteries is below 50% because for constructing batteries about equal amounts of hard antimonial lead and pure lead are required. The recycling ratio of old batteries is however usually higher than 50% and normally lies between 70 and 80%, so in the use of the above-described possibility there is a constantly growing excess of hard lead, finally leading to the need to sell most of the crude lead recovered from the reduction process on the market, when, more particularly because of the relatively high antimony content and the associated poor properties of the crude lead it has to be sold at relatively low prices.
The other possibility for recovery of lead suitable for construction of new batteries from crude lead recovered as described above consists in refining the crude lead itself to pure lead. However, this refining is relatively costly and because of the antimony content of the lead shows technical difficulties and moreover has as a consequence loss of the antimony contained in the crude lead.
Further disadvantages arise in both of the above-described possibilities and also in all other hitherto known ways of processing old batteries by the reduction with coal. Such reduction requires working temperatures of 800.degree. to 1000.degree. C and thus relatively high evaporation losses of lead as well as antimony arise. Particularly because of the antimony content of the scrap the reduction process results in volatile antimony oxide, causing great difficulties in the purification of the exhaust gases of the process necessary to prevent environmental pollution. The exhaust gases contain not only lead and lead oxide vapours but also considerable proportions of sulphur dioxide and, where the separation of the batteries leaving the impact mill is dispensed with and the plastics parts are burnt during smelting, also hydrochloric acid vapour and other volatile chloride vapours. Numerous and expensive measures are necessary to purify the exhaust gases. A further disadvantage of the antimony content of the scrap charge or the scrap components is the effect of the antimony compounds on the wall covering of the reduction oven, usually leading to the formation of dead hard, brittle compounds at the surface of the covering. These compounds are not resistant to alternating loads and thus after a relatively short service life result in failure of the covering and a necessity for its replacement.
In summary, in spite of the intensive efforts of experts charged with the problem of recovery of lead from used material and in spite of numerous proposals made specifically to improve the re-utilization of lead battery scrap, so far no process has been found for recovery, in a single process stage, of the two lead types, namely pure lead and hard antimonial or grid lead, which are required for the manufacture of new lead batteries, without involving costly separation and sorting processes and without also involving the disadvantages inherent in smelting battery scrap and the need for further processing steps subsequent to smelting, such as refining, alloying with antimony etc.